This property represents the first parameter associated with the destination.

The number of parameters and purpose of each varies depending on the EntryType of the Destination.

However in general they represent coordinates on the page which need be visible or aligned in some way.

For definitive details see:.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 151, page 366.

The fourth parameter of the destination. For FitR destinations it is the top edge of the fit rectangle, completing the four-coordinate bounding box.